Collaborative Research: Does sexual selection promote speciation and extinction? A test with Late Cretaceous Ostracoda from the US Gulf Coastal Plain

了解控制生物多样性起源和灭绝的因素是进化生物学的中心目标，与当今地球上生物多样性的保护和管理直接相关。最近的研究表明，物种形成(即新物种的进化)和灭绝可能会受到性选择的影响，性选择是个体相互竞争获得配偶的过程。到目前为止，对这一假设的检验还没有检验实际的物种形成和灭绝事件，而是依赖于替代指标，如现代物种的保护状态。在这里，研究人员利用被称为介形虫的微小甲壳类动物的丰富化石记录，测试了性别选择对物种形成和灭绝的影响。这些动物不同寻常，因为它们的性别可以从它们的贝壳中判断出来，甚至可以作为化石，研究人员可以使用雄性和雌性贝壳形状和大小的不同程度来衡量性别选择的强度。在这项研究中，研究人员将把介形虫物种的性别选择强度与物种形成和灭绝的模式联系起来，样本的时间跨度从8500万到6000万年前，沿着美国东南部从德克萨斯州到佐治亚州的狭长地带，在这段时间里，这些狭长地带位于海底。除了这项研究的科学目标外，研究人员还将指导一名博士后科学家作为教师和学者，并让多名本科生参与该项目。研究人员还将为史密森自然历史博物馆开展几项公共教育活动。技术描述了解物种灭绝和起源的机制是宏观进化理论的核心，并有助于解释生命的多样性和历史。最近的经验证据和理论模型表明，性选择是自然选择的一种形式，它根据交配成功的差异而起作用，可以同时推动物种形成和灭绝。到目前为止，性别选择与物种灭绝或物种形成之间的联系的测试在很大程度上依赖于新的数据，并使用实际宏观进化事件的弱替代品，如保护状态(物种灭绝)或支系丰富度(物种形成)。在这里，该项目利用了丰富的介形类化石记录，并提议进行第一次检验性二型性是否与实际灭绝和物种灭绝的不同比率有关。这项研究首次测试了宏观进化假说，即性选择与物种形成和灭绝都是正相关的，重点是美国墨西哥湾海岸平原(GCP)晚白垩世至古新世介形类保存完好和采样良好的记录。具体地说，该项目将：(1)使用基于轮廓的形态计量学来衡量性别二态的程度--性选择的代理？；(2)记录白垩纪晚期和古新世早期经过分类审查的介形虫物种的地层范围；(3)使用基于似然的模型拟合，测试性别二态对物种起源或灭绝倾向的影响。

Nontechnical AbstractUnderstanding the factors that control the origin and extinction of biodiversity is a central goal of evolutionary biology and is directly relevant to the conservation and management of biodiversity on the Earth today. Recent research suggests that speciation (i.e., the evolution of new species) and extinction can be affected by sexual selection, a process that occurs when individuals compete with each other for access to mates. To date, tests of this hypothesis have not examined actual speciation and extinction events, relying instead on proxies, such as the conservation status of modern species. Here the researchers test the effects of sexual selection on speciation and extinction using the rich fossil record of tiny crustaceans called ostracodes. These animals are unusual because their sex can be determined from their shells, even as fossils, and the researchers can use the extent to which males and females differ in shell shape and size as a measure of the intensity of sexual selection. In this research, the researchers will relate the strength of sexual selection in ostracode species to patterns of speciation and extinction in samples that span a time interval from 85 to 60 million years ago along a swath of the southeastern United States from Texas to Georgia that was under the sea during this time period. In addition to the scientific goals of this research, the researchers will mentor a post-doctoral scientist as both a teacher and scholar, and involve multiple undergraduate students in the project. The researchers will also develop several public education activities for the Smithsonian Museum of Natural History.Technical DescriptionUnderstanding the mechanisms that underlie species extinction and origination is central to macroevolutionary theory and helps to explain the diversity and history of life. Recent empirical evidence and theoretical models suggest that sexual selection, a form of natural selection that acts upon variation in mating success, can drive both speciation and extinction. To date, tests of the association of sexual selection with either extinction or speciation have relied heavily on neontological data and use weak proxies of actual macroevolutionary events, such as conservation status (for extinction) or clade richness (for speciation). Here the project capitalize on the rich fossil record of ostracodes and propose to perform the first examination of whether sexual dimorphism, an indicator of the strength of sexual selection, is associated with differential rates of actual extinction and speciation.The research provides the first test of the macroevolutionary hypothesis that sexual selection is positively association with both speciation and extinction, focusing on the well-preserved and well-sampled record of Late Cretaceous through Paleocene ostracodes on the US Gulf Coastal Plain (GCP). Specifically, the project will: (1) measure the magnitude of sexual dimorphism?a proxy for sexual selection?using outline-based morphometrics; (2) document the stratigraphic ranges of taxonomically vetted ostracode species from the Late Cretaceous and early Paleocene; (3) test, using likelihood-based model fitting, the influence of sexual dimorphism on the propensity of species to originate or go extinct.